On account of its high thermal conductivity in comparison to nickel-based alloys, the stationary components of the first turbine stage are made in part of cobalt-based alloys such as MAR-M 509. This is the case both for static gas turbines and for aero engines.
For cohesive joining connections at these components, which are made in the form of high-temperature soldered joints, the primary materials are nickel-based solders. These conventional nickel-based solders contain boron and/or silicon as melting point depressant. As a consequence of the different thermal expansion coefficients of cobalt and of nickel, high residual stresses can arise in the region of the joining zone, which can lead to a weakening of the assembly. In addition, in the case of wide joining gaps and short soldering process times, brittle phases can precipitate out in the soldering gap, which phases can additionally impair the mechanical integrity.
Hitherto, for joining Co-based materials, use was made of conventional nickel-based solders. In that context, a significant impairment of the mechanical properties in the region of the joining zone was accepted.